The invention relates to a backlight module and, more particularly, relates to an illumination device thereof.
Conventionally, backlight modules are disposed at the rear of display panels in liquid crystal displays (LCDs), providing backlight to the display panels. Backlight modules are normally direct type or side-light type, comprising a light source such as a cold cathode fluorescent lamps (CCFLs). The direct backlight module comprises a plurality of lamps with luminous flux increased by increasing the number of lamps. Thus, the direct backlight module is mostly utilized in a large-sized LCD, providing required light intensity.
The weight and thickness of the LCDs, however, increase accordingly. Since compact LCDs are currently popular, the conventional backlight module is not suitable. Side-light modules comprise a light source disposed at an edge of the module and requires a light guide plate for uniform distribution. Thus, the side-light module is more suitable for a small LCD. The light intensity emitted from the edge thereof, however, is less.
The weight of a CCFL increases with the number of lamps. Thus, another type of light source such as light emitting diodes (LEDs) replaces the CCFL for reduced weight, providing increased light intensity and lifetime. The light path of LEDs, however, is linear within a small light emitting range. Thus, a large number of LEDs must be utilized together to provide sufficient light intensity. If the arrangement and relative position of each LED varies slightly, the color of the light can be changed and light intensity reduced accordingly.
As shown in FIG. 1A, the backlight module 1 comprises a frame 15, a plurality of optical films 11, a light diffusion sheet 12, a plurality of reflective plates 13, and a plurality of light sources 14. The optical films 11, the light diffusion sheet 12, and the reflective plates 13 are connected via the frame 15. The light sources 14 are disposed over the reflective plate 13, emitting light toward the panel, as indicated by arrow L. A portion of light is reflected by the reflective plate 13, and light passing through the light diffusion sheet 11 is emitted toward the panel (not shown).
As described, the conventional backlight module 1 has a problem in that the light emitted by the LED travels in a linear direction. That is, most of the light is emitted in the panel direction. Thus, the light is not uniformly distributed. The light intensity difference between the light source 14 and the reflective plate 13 is high, causing uneven image intensity. To solve the problem, more light sources are required and must be compactly arranged such that the weight and manufacturing costs are increased, as well as temperature in the backlight module.
A side emitting type LED 14′ solves the problem of the linear light path, as shown in FIG. 1B. The side emitting type LED 14′ comprises an LED body 140, a base 141, and an electrical isolation stripe 143. The side emitting type LED 14′ allows 80% of the light to be emitted sideways, in the direction of the arrow, however, the structure and manufacturing steps are complicated, and costs are higher. Additional light guide plate 15, reflective metal sheet 18 and other optical films are required and disposed around the LED 14′ to mix and reflect the light uniformly, increasing total cost and weight.